The above-identified devices comprise a generator containing in the same case various electronic circuits and an energy source. When such devices are implanted, the generator is mechanically and electrically connected to a probe equipped with electrodes for intracardiac stimulation, making it possible to detect depolarization potentials of the myocardium and to deliver stimulation impulses produced by the generator.
The probe connection must be capable of being detected automatically by the generator, so as to activate various functionalities, e.g., launch algorithms, initialize a certain number of parameters, and memorize starting data. U.S. Pat. Nos. 5,522,856 and 5,370,666 disclose an insertion of the probe by uninterrupted screening of terminals of a connector head of the device and measurement of the impedance between these terminals. In the absence of a probe, this impedance is extremely high, but upon insertion of a probe the value decreases below a certain threshold whose crossing, when detected, causes the pacemaker to change from a sleeping mode to a completely functional mode. Continuous screening of the impedance, however, impacts energy consumption and lifespan of the battery, because it requires with each measurement injection of a current between terminals of the probe and activation of circuits for measuring the corresponding collected voltage. Another possibility consists of using an external programmer to activate the generator at the end of an implantation. This technique, however, requires intervention of a surgeon.
One of the goals of the present invention is to propose a circuit that can automatically detect connection of a probe, without requiring direct and permanent measurement of the impedance between terminals, and without recourse to an external programmer.
In addition, it is generally possible to connect to the same generator two different types of probes, monopolar or bipolar, at the choice of the surgeon and according to the type of pathology to be treated. In the case of a monopolar (or “unipolar”) probe, detection and stimulation are operated between the single electrode and the metal case of the generator, while in a bipolar probe, detection and stimulation can be carried out either in a differential mode between two electrodes of the probe, or in a common mode between the case of the generator and one or the other of the probe electrodes. Of course, many internal parameters of the generator must be selected according to the type of probe used, monopolar or bipolar, e.g., commutation of the terminals having to be used, collection of depolarization signals, adjustment of stimulation parameters, and modification of the algorithms controlling the microprocessor. Any error in selecting the type of operating mode (monopolar or bipolar) can involve serious consequences. For example, if the device is programmed for a bipolar stimulation, but is equipped with a monopolar probe, this error can cause a loss of capture and application of an inappropriate stimulation, with a risk for the patient.
Another goal of the present invention is to propose a device that can, in addition to automatically detecting connection of a probe, determine the type of probe being used, i.e., monopolar or bipolar, and upon doing so, commutate and parameterize appropriate circuits and algorithms of the device. This function, managed automatically by the device, makes it possible to minimize, if not avoid, any risk of error resulting from non-conformance between type of probe used and operating mode of the device. One thus avoids, for example, any risk of bipolar stimulation applied erroneously to a monopolar probe.
Automatic determination of the type of polarity also makes it possible to take into account the fact that in the majority of countries the pacemaker is delivered in unipolar configuration, to ensure a stimulation in any event. But today in many cases it is a bipolar probe that is implanted, which requires parameterization of the generator only after the probe is connected. The system according to the present invention, by automatically determining the polarity to be used upon implantation of the device, authorizes an automatic setting of the parameters of the generator without requiring intervention of the surgeon.
Another goal of the invention is to propose a device making it possible to take into account the particular configuration where the probe was implanted and connected to the case of the pacemaker, but where this case is not yet introduced into the implantation site (i.e, the incision or pocket in the patient into which the surgeon plans to place the impulse generator). The case is thus not yet in contact with tissues of the patient and cannot be used as a reference potential. In such a situation it is preferable to avoid a monopolar stimulation of the probe, because the delivered impulses would be ineffective due to absence of a ground. However, during this intermediate phase, it is desirable to deliver a bipolar stimulation if a ventricular bipolar probe is implanted and already connected.
The device of the present invention makes it possible to take into account this intermediate configuration, until implantation of the device. It is only after detection of the implantation that the corresponding functions of the pacemaker will be activated, and the polarity configured, i.e., monopolar or bipolar. Due to the automatic activation of the pacemaker functionalities, the surgeon will never need to force a particular mode of stimulation before implantation of the generator in the pocket, or after completion of implantation. It will be sufficient for the surgeon to connect the probe, whatever its type, with the generator, and safety will be automatically ensured during and after the intervention.